Conventionally, it is known a process for industrially producing (meth)acrylic acid by gas-phase catalytic oxidation of a (meth)acrylic acid production raw material. (Meth)acrylic acid-containing gas generated by gas-phase catalytic oxidation of the (meth)acrylic acid production raw material is, for example, collected by a liquid medium to be recovered as a crude (meth)acrylic acid solution, and then, the crude (meth)acrylic acid solution is purified by methods such as distillation, diffusion, extraction, crystallization, or the like.
For purifying crude (meth)acrylic acid by crystallization, it is generally known that a dynamic crystallization apparatus or a static crystallization apparatus is employed, for example. As a method for purifying a crude methacrylic acid solution by crystallization, Patent Literature 1 discloses a method of crystallizing and melting of a crude methacrylic acid solution to purify, for example. In Patent Literature 1, melting is performed in twice, and the melt obtained by the first melting (a sweating step) is discharged from the system and the melt obtained by the second melting is recovered as purified methacrylic acid. Patent Literature 2 discloses a dynamic crystallization apparatus having a plurality of projections on a surface on which a crystal is formed in order to prevent dropping of the crystal at the time of crystallization and quickly melt the crystal. Patent Literature 3 discloses a method for carrying out crystallization of acrylic acid using a crystallization apparatus equipped with a scraping means, in which melted acrylic acid mixed with a polymerization inhibitor is circulated and supplied to a crystal in order to prevent polymerization of purified acrylic acid.